← Het Tet Yodh →
Phoenician Hebrew ט Aramaic Syriac ܛ Arabic ط
Phonemic representation	tˤ
Position in alphabet	9
Numerical value	9
Alphabetic derivatives of the Phoenician
Greek Θ Latin - Cyrillic Ѳ

Teth, also written as Ṭēth or Tet, is the ninth letter of the Semitic abjads, including Phoenician Ṭēt , Hebrew Ṭēt ט, Aramaic Ṭēth , Syriac Ṭēṯ ܛ, and Arabic Ṭāʾ ط. It is 16th in modern Arabic order. The Persian Ța is pronounced as a hard "t" sound and is the 19th letter in the modern Persian alphabet. The Phoenician letter also gave rise to the Greektheta (Θ), originally an aspirated voiceless alveolar stop but now used for the voiceless dental fricative.

Origins[edit]

Kalimah Tayyibah: Kalimah Tayyibah kalimat aṭ-ṭaiyibah (Word of Purity)

In English:

lā e la ha el lal la ma ha ma dur ra su lal la

English Translation:

There is none worthy of worship but Allah, and Muhammad is the messenger of Allah.

Hebrew Tet[edit]

Orthographic variants
Serif	sans-Serif	Monospaced	Cursive Hebrew	Rashi script
ט	ט	ט

Hebrew pronunciation[edit]

Significance[edit]

Arabic Ṭāʾ[edit]

Similar symbols[edit]

A symbol similar to the Phoenician teth is used for the tensor product, as , but this is presumably an independent development, by modification of the multiplication sign ×. The Hebrew ט is also visually similar to the letter Ʋ.

Ø (disambiguation).

Look up Θ or θ in Wiktionary, the free dictionary.

Greek alphabet
Αα Alpha Νν Nu Ββ Beta Ξξ Xi Γγ Gamma Οο Omicron Δδ Delta Ππ Pi Εε Epsilon Ρρ Rho Ζζ Zeta Σσς Sigma Ηη Eta Ττ Tau Θθ Theta Υυ Upsilon Ιι Iota Φφ Phi Κκ Kappa Χχ Chi Λλ Lambda Ψψ Psi Μμ Mu Ωω Omega
History
Archaic local variants Diacritics Ligatures Numerals ϛ (6) ϟ (90) ϡ (900)
Use in other languages
Bactrian Coptic Albanian
Related topics
Use as scientific symbols
Book  Category  Commons
v t e

Theta (uppercase Θ or Ө, lowercase θ (which resembles digit 0 with horizontal line) or ϑ;Ancient Greek: θῆτα, thē̂ta, [tʰɛ̂ːta]; Modern: θήτα, thī́ta, [ˈθita]; UK /ˈθiːtə/, US /ˈθeɪtə/) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth . In the system of Greek numerals it has a value of 9.

Contents

  [hide] 

• 1 Greek
  • 1.1 Forms
• 2 Latin
• 3 Cyrillic
• 4 International Phonetic Alphabet
• 5 Mathematics and science
  • 5.1 Lower case
  • 5.2 Upper case
• 6 In its archaic form
  • 6.1 Greek mathematics
• 7 Symbolism
  • 7.1 Abbreviation
• 8 Character Encodings
• 9 See also
• 10 Notes

Greek[edit]

The alphabet on a black figurevessel, with a point-and-circle theta.

In Ancient Greek, θ represented the aspirated voiceless dental plosive /t̪ʰ/, but in Modern Greek it represents the voiceless dental fricative /θ/.

Forms[edit]

"θ" redirects here. For the letter used in IPA, see Voiceless dental fricative.

In its archaic form, θ was written as a cross within a circle ( or ), and later, as a line or point within a circle ( or ).

The form ϑ was retained by Unicode as U+03D1 ϑ "GREEK THETA SYMBOL" ("=script theta"), separate from U+03B8 θ "GREEK SMALL LETTER THETA". For the purpose of writing Greek text, the two can be font variants of a single character, but θ and ϑ are also used as distinct symbols in technical and mathematical contexts.

Latin[edit]

The name ARAÐÐOVNA on a Gaulish tombstone.

In the Latin script used for the Gaulish language, theta developed into the tau gallicum, conventionally transliterated as Ð, although the bar extends across the centre of the letter. The phonetic value of the tau gallicum is thought to have been [t͡s].

Cyrillic[edit]

The early Cyrillic letter fita (Ѳ, ѳ) developed from θ.

International Phonetic Alphabet[edit]

In the International Phonetic Alphabet, [θ] represents the voiceless dental fricative, as in thick orthin. It does not represent the consonant in the, which is the voiced dental fricative.

Mathematics and science[edit]

This section does not cite any references or sources. Please help improve this section byadding citations to reliable sources. Unsourced material may be challenged and removed.(January 2011)

Lower case[edit]

The lower-case letter θ is used as a symbol for:

• A plane angle in geometry.
• A special function of several complex variables.
• One of the Chebyshev functions in prime number theory.
• The potential temperature in meteorology.
• The score of a test taker in item response theory.
• Theta Type Replication: a type of bacterial DNA replication specific to circular chromosomes.
• Threshold value of an artificial neuron.
• A Bayer designation letter applied to a star in a constellation; usually the eighth star so labelled but not necessarily the eighth brightest as viewed from Earth.
• The parameter frequently used in writing the likelihood function (Bayes theorem).
• The Watterson estimator for the population mutation rate in population genetics.
• Indicates a minimum optimum integration level determined by the intersection of GG and LL schedules. The GG-LL schedules are a tool used in analyzing the potential benefits of a country pegging their domestic currency to a foreign currency.
• The reserve ratio of banks in economic models.
• The ordinal collapsing function developed by Solomon Feferman^[1]

Upper case[edit]

The upper-case letter Θ is used as a symbol for:

• Quantity or temperature, by SI standard (in italics).
• Dimensionless temperature in transport phenomena.
• An asymptotically tight bound in the analysis of algorithms (big O notation).
• A certain ordinal number in set theory.
• Pentaquarks, exotic baryons in particle physics.
• A brain signal frequency (beta, alpha, theta, delta) ranging from 4–8 Hz.
• One of the variables known as "Greeks" in finance, representing the lost-value rate of an option over time.
• A variable indicating temperature difference in heat transfer.

In its archaic form[edit]

• In its archaic form () theta is used as a symbol for Earth.

Greek mathematics[edit]

The common usage of theta in mathematical problems began with the Greeks. They logically chose this Greek symbol since it was the next in their alphabet not yet used and was easily legible when recreating for multiple uses.

Archaic crossed forms of theta are seen in the wheel letters of Linear A, Linear B, and Egyptian hieroglyphics, the mathematical tensor product, exclusive disjunction, and direct sum operators, the identification symbol for the Earth (as already mentioned), and the Celtic cross. The circumpunct, or circled dot, is seen in a wide range of places.

Symbolism[edit]

θ (θάνατος, death) in a mosaic

• In ancient times, Tau was used as a symbol for life or resurrection, whereas the eighth letter of the Greek alphabet, theta, was considered the symbol of death.

According to Porphyry of Tyros, the Egyptians used an X within a circle as a symbolof the soul; having a value of nine, it was used as a symbol for Ennead. Johannes Lydus says that the Egyptians used a symbol for Kosmos in the form of theta, with a fiery circle representing the world, and a snake spanning the middle representing Agathos Daimon (literally: good spirit).^[2]

The Egyptians also used the symbol of a point within a circle (, the sun disc) to represent the sun, which might be a possible origin of its use as the Sun'sastrological glyph. It is worthwhile to note that θῆτα (theta) has the same numerical value in isopsephy as Ηλιος (Helios): 318.

Abbreviation[edit]

In classical Athens, it was used as an abbreviation for the Greek θάνατος (thanatos, “death”) and as it vaguely resembles a human skull,^{[citation needed]} theta was used as a warning symbol of death, in the same way that skull and crossbones are used in modern times. It survives on potsherds used by Athenians when voting for the death penalty.^[2] Petrus de Dacia in a document from 1291 relates the idea that theta was used to brand criminals as empty ciphers, and the branding rod was affixed to the crossbar spanning the circle.^[3] For this reason, use of the number theta was sometimes avoided where the connotation was felt to be unlucky - the mint marks of some Late Imperial Roman coins famously have the sum ΔΕ or ΕΔ (delta and epsilon, that is 4 and 5) substituted as a euphemism where a Θ (9) would otherwise be expected.